Brain and Language

Brain and Language

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Brain and Language

(Jesús Ramos Fernández)

The Human Brain:

The brain is the most complex organ of the body. It is composed of cerebral hemispheres, one on the right, and one on the lef, joined by the corpus callosum, a network of 2 million fibes.

The modularity of the Brain:

Since the middle of the nineteen century, scientists have assumed that it is possible to discover the particular bran areas where language capacities (Competence and performance) are localized.

Language was the first cognitive model to be localized in the brain via scientific evidence. In 1864, Paul Broca related language specifically to the left side of the brain. He based his finding on the observation that damage to the front part of the left hemisphere (now called Broca’s area, or region) resulted in loss of speech, whereas damage to the right side did not. Language, then, is lateralized, the term used to refer to any cognitive function that is localized primarily on one side of the brain or the other.

Today, patients with injuries to Broca’s area may have Broca’s aphasia. Aphasia is the neurological term for any language disorder that results from brain damage caused by disease or trauma. Persons with Broca’s aphasia may have labors speech, word-finding pauses, disturbed words orders, and difficulties with function words such as “to” and “if”. Language understanding may not appear abnormal, but controlled tests reveal a loss of comprehension of complex or ambiguous sentences.

In 1874 thirteen years after Broca’s Paris paper, Carl Wernicke presented a paper that described another variety of aphasia that occurred in patients with lesions in the back portion of the left hemisphere, now known as Wernicke’s area, or region. Unlike Broca’s patients, those with Wernicke’s aphasia spoke fluently with good intonation and pronunciation, but with numerous instances of lexical errors (words substitutions), often producing jargon and nonsense words. They also had difficulty in comprehending speech.

Evidence from childhood brain lesions:

The study of children with prenatal, perinatal, or childhood brain lesions suggest that although lateralization of language to the left hemisphere is a process that begins very early in life, language may be less lateralized initially, with the right hemisphere also playing some role. Studies of hemiplegic children -those with lesions in one side of the brain- show differential cognitive abilities. Those with the damaged left hemispheres show greater deficiency in language acquisition and performance with the greatest impairments in their ability to form words and sentences.

In extreme cases of disease, it may be necessary to surgically remove one hemisphere of the brain. When this happens, the remaining hemisphere attempts to take over functions of the missing one. Mature patients who have their rights hemispheres excised retain their language abilities, thought other cognitive losses may results.

It appears than even from birth the human brain is predisposed to specialize for language in the left hemisphere since language usually does not develop normally in children with early left-hemisphere brain lesions.

Split Brains:

Split-brain patients also provide evidence for language lateralization and for understanding brain functions. Surgeon cut through the corpus callosum, the fibrous network that connects the two halves, When this pathway in broken, there is no communication between the “two brains.”

Studies of split-brain patients reveal that in the human brain, as in the monkey brain, the two hemispheres are distinct. Moreover, messages sent to the two sides of the brain result in different responses, depending on which side receives the message. Sensory information arrives in the opposite side of the brain from the side of the body that sends it. In a split-brain patient, information in the right hemisphere is inaccessible to the left hemisphere. If an apple is placed in the left hand of a split-brain human whose eyes are closed, the person qm use it appropriately but cannot name it. The right brain senses the apple and distinguishes it from other objects, but the information cannot be relayed to the left brain for linguistic naming. By contrast, if an apple is placed in the right hand, the subject is immediately able to name it as well as to describe it.

Various experiments of this sort have provided information on the different capabilities of the two halves. The right brain does better than the left in pattern-matching tasks, in recognizing faces, and in spatial orientation. The left hemisphere is superior for language, for rhythmic perception, for temporal-order judgments, and for mathematical thinking.

Further experiments:

Dichotic listening is an experimental technique that uses auditory signals to observe the behavior of the individual hemispheres of the human brain. Subjects hear two different sound signals simultaneously through earphones. They may hear curl in one ear and girl in the other, or a cough in one ear and a laugh in the other. When asked to state what they heard in each ear, subjects are more frequently correct in reporting linguistic stimuli (words, nonsense syllables, and so on) delivered directly to the right ear, but are more frequently correct in reporting nonverbal stimuli (musical chords, environmental sounds, and so on) delivered to the left ear.

Both hemispheres receive signals from both ears, but the contralateral stimuli outweigh the ipsilateral (same side) stimuli because they are more intense and arrive more quickly. The accuracy with which subjects report what they heard is evidence that the left hemisphere is superior for linguistic processing, and the right hemisphere is superior for nonverbal information.

These experiments are important because they show not only that language is lateralized, but also that the left hemisphere is not superior for processing all sounds, only for those that are linguistic.

More Evidence for Modularity

In September 1848 Phineas Gage became a famous figure in medical history. He achieved medical immortality when an explosion drove a four-foot-Iong iron rod through his head. Despite the gaping tunnel in his brain, Gage maintained the ability to speak and understand, and retained whatever intellectual abilities he had before the injury. However,